JavaScript中如何对库存对象做数量扣减后生成新对象

核心逻辑：遍历全量库存品类，对应品类有预留量的就扣减对应数值，无预留量的保留原库存数值即可。

基础兼容版实现（兼容所有JS运行环境） #

var availability = {"bike":10,"cycle":3,"car":1};
var reserved ={"cycle":1,"bike":10};

var response = {};
for (var goodsType in availability) {
  // 无对应预留量时默认取0，避免出现NaN
  var reserveNum = reserved[goodsType] || 0;
  response[goodsType] = availability[goodsType] - reserveNum;
}

// 输出结果：{"bike":0,"cycle":2,"car":1}
console.log(response);

ES6+ 简洁版实现 #

const availability = {"bike":10,"cycle":3,"car":1};
const reserved ={"cycle":1,"bike":10};

const response = Object.fromEntries(
  Object.entries(availability).map(([type, stock]) => [type, stock - (reserved[type] ?? 0)])
);

补充：如果业务需要避免库存被扣减为负数，可以将扣减逻辑替换为 Math.max(0, stock - (reserved[type] ?? 0))。

内容的提问来源于stack exchange，提问作者Pavan k